Within the last few years, the music world has witnessed the birth and increasing popularity of a new type of composer/performer known as a “turntablist”. Generally, a turntablist performs a musical piece by manually rotating one or more conventional phonographic records to generate musical sounds.
FIG. 1 is a schematic block diagram of a conventional sound system 10 that is used by many of today's turntablists. The system 10 includes a pair of turntables 12 and 14, which amplify the sounds from respective phonographic records 13 and 15. The turntables 12 and 14 respectively provide first (PGM1) and second (PGM2) program audio signals to an audio mixer 16, which mixes these signals together to generate a mixed master audio signal (MASTER). An optional effects box 18 generates a signal (MASTER EFFECTS) by adding audio effects to the MASTER signal. Typically, the PGM1, PGM2, MASTER, and MASTER EFFECTS signals are stereo signals having respective left (L) and right (R) components. A house amplifier 20 amplifies the MASTER EFFECTS signal and provides its L and R components to speakers 22 and 24, respectively.
FIG. 2 is a control panel 26 of the mixer 16 of FIG. 1. The mixer 16 includes gain controls 28 and 30 for respectively adjusting the gains of the PGM1 and PGM2 signals (FIG. 1) over their entire frequency ranges, bass controls 32 and 34 for respectively adjusting the gains of the low-frequency components of PGM1 and PGM2, and treble controls 36 and 38 for respectively adjusting the gains of the high-frequency components of PGM1 and PGM2. Because the turntables 12 and 14 (FIG. 1) may provide PGM1 and PGM2 with different gains, the controls 28 and 30 allow the turntablist to compensate for these gain differences so that PGM1 and PGM2 have the same amplitude characteristics before the mixer 16 processes them further. Additionally, the turntablist may set the controls 32, 34, 36, and 38 to attenuate or amplify the bass or treble-bands of PGM1 and PGM2, respectively. For example, the turntablist may want to isolate a singing voice from the record 13. Because the frequency components of a human voice lie mainly in the mid band between the bass and treble-bands, the turntablist adjusts the controls 32 and 36 for full attenuation, i.e., “cut”, so that ideally only the mid-band frequency components of PGM1 are audible in the MASTER EFFECTS signal (or the MASTER signal if the effects box 18 is not included in the system 10).
The mixer 16 also includes input-fader controls 40 and 42 for adjusting the volumes of PGM1 and PGM2—as heard in the MASTER signal—after PGM1 and PGM2 have been processed by the amplification circuitry controlled by the controls 28, 30, 32, 34, 36, and 38. Typically, the fader controls 40 and 42 are respective sliding controls, such as sliding potentiometers, that the turntablist uses to vary the respective volumes of PGM1 and PGM2 for musical effect while he is playing his piece.
FIG. 3 is a plot of a curve 43, which shows the attenuation in decibels (dB) of PGM1 and PGM2 versus the control position for a known version of the input-fader controls 40 and 42, respectively, of FIG. 2. For clarity here and below, the characteristics and operation of the control 40 are discussed, it being understood that the characteristics and operation of the control 42 are similar. In operation, referring to both FIGS. 2 and 3, if the control 40 is in the “0”, i.e., cutoff, position, then the volume of PGM1 is −100 dB, i.e., 100 dB down, and for all practical purposes PGM1 has zero volume and is thus inaudible in the MASTER EFFECTS signal. Conversely, if the control 40 is in the “10”, i.e., full, position, then the volume of PGM1 is 0 dB, which is full volume in this version of the control 40.
Referring to FIGS. 2 and 3, the mixer 16 may include reversal controls (not shown in FIG. 2)—one for each of the controls 40 and 42—for reversing the cutoff and full positions of the controls 40 and 42, respectively. Such controls are known as “hamsters” in turntablist jargon, and are included so that the turntablist can attain the most comfortable hand positions while performing his piece. In operation, if the reversal control is in one position, then the “0” position of the control 40 is the cutoff position and the “10” position is the full position as discussed above. Conversely, if the reversal control is in another position, then the “0” position is the full position and the “10” position is the cutoff position.
Referring again to FIGS. 2 and 3, the mixer 16 may include contour controls (not shown in FIG. 2)—one for each of the controls 40 and 42—for adjusting the shape of the curve 43. Contour controls typically allow the turntablist more flexibility in playing his musical piece. In operation, a change in the shape of the curve 43 changes the distance that the turntablist must move the control 40 to get a given change in the volume of PGM1. For example, the turntablist may want to transition PGM2 from cutoff to full volume by moving the control 40 only a fraction of the distance between the “0” and “10” positions instead of the entire distance as the illustrated shape of the curve 43 requires. Therefore, the turntablist sets the contour control such that the curve 43 has a shape that is steeper in the cutoff region than illustrated in FIG. 3.
Referring again to FIG. 2, the mixer 16 also includes a crossfader control 44 for adjusting the ratio of the volume of PGM1 to the volume of PGM2—the volumes of PGM1 and PGM2 also being set by the fader controls 40 and 42, respectively—in the MASTER signal. Like the fader controls 40 and 42, the crossfader control 44 is typically a sliding control that the turntablist uses to vary this volume ratio for musical effect while he is playing his piece.
FIG. 4 is a plot of curves 45 and 46, which respectively show the attenuation in decibels for PGM1 and PGM2 versus the control position for a known embodiment of the crossfader control 44. In operation, referring to both FIGS. 2 and 4, if the control 44 is all the way to the left in the PGM1“10”/PGM2“0” position, i.e., full position for PGM1 and cutoff position for PGM2, then the volume of PGM1 is full and the volume of PGM2 is 100 dB down, and for all practical purposes PGM1 is the only audible component of the MASTER EFFECTS signal. Conversely, if the control 44 is all the way to the right in the PGM1 “0”/PGM2 “10” position, i.e., cutoff position for PGM1 and full position for PGM2, then the volume of PGM1 is 100 dB down and the volume of PGM2 is full, and for all practical purposes PGM2 is the only audible component of the MASTER EFFECTS signal.
The mixer 16 may also include a reversal control, i.e., “hamster” (not shown in FIG. 2), for reversing the cutoff and full positions of the control 44 with respect to PGM1 and PGM2. In operation, if the reversal control is in one position, then the leftmost position of the control 44 is the PGM1-full/PGM2-cutoff position and the rightmost position is the PGM1-cutoff/PGM2-full position as discussed above. Conversely, if the reversal control is in another position, then the leftmost position of the control 44 is the PGM1-cutoff/PGM2-full position and the rightmost position is the PGM1-full/PGM2-cutoff position.
Still referring to FIGS. 2 and 4, the mixer 16 may also have a contour control (not shown in FIG. 2) for adjusting the shapes of the curves 45 and 46 in a manner similar to that discussed above for adjusting the shape of the curve 43 of FIG. 3. Furthermore, the illustrated shapes of the curves 45 and 46 may represent a constant-power crossfader contour. In other words, regardless of the position of the crossfader control 44, the sum of the powers, and thus the volumes, of PGM1 and PGM2 in the MASTER EFFECTS signal equals a constant level.
Unfortunately, movement of the fader controls 40 and 42 often adds audible levels of noise called “travel” noise, to PGM1 and PGM2, respectively. Additionally, because they are in the respective PGM1 and PGM2 signal paths, the fader controls 40 and 42 may allow audible levels of PGM1 and PGM2 to “bleed into” the MASTER EFFECTS signal even if the controls 40 and 42, respectively, are in their full-cut positions.
One way to reduce both travel noise and signal bleed through is to use high quality, low-noise controls, such as low-noise potentiometers, for the controls 40 and 42. But these low-noise potentiometers are relatively expensive, and, like their cheaper counterparts, soon wear down to a point where they generate unacceptable travel noise or allow unacceptable signal bleed through, and thus must be replaced.
Another way to reduce the travel noise is to remove the input-fader controls 40 and 42 from the PGM1 and PGM2 signal paths, respectively. Thus the output signals from the controls 40 and 42 can be filtered and then used to control the gain of an audio amplifier. Unfortunately, such designs are frequently expensive, complex, and lack the consistent performance required by turntablists. For example, the filter may cause the controls 40 and 42 to exhibit inappropriate volume-increase and volume-decrease rates—often called “attack” and “decay” rates, respectively—which may compromise the ability of the filter to remove travel noise without adversely altering the performance of the turntablist. In addition, such designs frequently require a separate gain-controlled amplifier for each fader control 40 and 42, thus making the input-fader circuit too complex and expensive for compact performance mixers.
The crossfader control 44 may also add audible levels of travel noise and signal “bleed” to PGM1 and PGM2. Noise-reduction techniques similar to those discussed above for the controls 40 and 42 may be used to reduce the travel noise generated by the crossfader control 44. Unfortunately, these techniques often exhibit the same shortcomings as the above-described techniques.
Furthermore, many crossfader contour controls lack a constant-power setting. And like the input-fader circuits, the crossfader circuit may allow audible levels of PGM1 and PGM2 to bleed into the MASTER EFFECTS signal even if the control 44 is in its respective PGM1-full-cut or PGM2-full-cut position.
Furthermore, the input-fader circuits are often highly sensitive to component tolerances such that the same absolute positions of the respective controls 40 and 42 may provide different attenuations for different mixers 16. For example, suppose that controls 40 of two mixers 16 are in their respective “6” positions. Because of the high sensitivities of the respective input-fader circuits, however, the first mixer may attenuate PGM1 by 20 dB and the second mixer may attenuate PGM1 by 18 dB. Often, the turntablist practices on one mixer 16 and performs on another mixer 16, and is, therefore, used to the position-attenuation characteristics for the controls 40 and 42 of the practice mixer. Consequently, if the position-attenuation characteristics of the performance mixer are different than those of the practice mixer, then the performed piece will not sound as the turntablist intended. Thus, differences in the input-fader position-attenuation characteristics between the practice and performance mixers can ruin the turntablists performance!
Like the input-fader circuits, the crossfader circuit is often highly sensitive to component tolerances, and thus may cause the crossfader control 44 to exhibit different position-attenuation characteristics from mixer to mixer. Moreover, because the design of the crossfader circuit is often complex, the crossfader circuit often requires a relatively large number of components and thus contributes significantly to the cost, size, and power consumption of the mixer 16.
Furthermore, referring to FIG. 1, if the turntablist wants to use the effects box 18 to add audio effects to either PGM1 or PGM2, then he must disconnect the box 18 from MASTER and reconnect it between the respective turntable 12 or 14 and the mixer 16. This makes it virtually impossible for the turntablist to add effects to more than one of the PGM1, PGM2, and MASTER signals while he plays his piece. One solution is to use three effects boxes 18: one for PGM1, one for PGM2, and one for MASTER. But unfortunately, because the effects box 18 is a relatively expensive item, most turntablists can afford to have only one.
Moreover, to allow independent gain control of the bass and treble frequency components, the mixer 16 often includes bass-band, mid-band, and treble-band filters, which are collectively called a tone-control circuit or simply a tone control. Unfortunately, the frequency cutoff slopes of many tone-control circuits are not steep enough to allow for such independent gain control. One solution is to use a 4th-order tone-control circuit. But the filters used in a 4th-order tone-control circuit often have relatively large numbers of components, and thus often increase the cost, size, and power consumption of the mixer 16.